A low-dropout (LDO) regulator is a direct current (DC) linear voltage regulator capable of regulating its output voltage even when the supply voltage is very close to the output voltage. Compared to other types of DC to DC regulators, LDO regulators may exhibit a smaller overall size since no large inductors or transformers are required. Further, compared to switching regulators, there is no switching noise as no switching takes place in typical LDO regulators. Finally, as LDO regulators typically consist of a reference voltage source, an amplifier, and a pass element, the simplicity of the regulator design should be mentioned as an additional benefit of LDO regulators.
When LDO regulators are used to power noise sensitive analog circuits, noise reduction becomes important in the design process. Such noise sensitive analog circuits may include e.g. analog-to-digital converters, digital-to-analog converters, voltage-controlled oscillators, phase-locked loops, and high-speed clocks. For example, if an LDO regulator is used to provide a supply or reference voltage to a 12 bit, 16 bit or 18 bit analog-to-digital converter, the accuracy of the least significant bit LSB may severely depend on the accuracy of the supply or reference voltage provided by the LDO regulator.